1. Field of the Invention
The present invention relates to apparatus and methods for inspection or review of substrates, such as semiconductor wafers and masks.
2. Description of the Background Art
Low energy electron microscopy (LEEM) imaging systems which utilize electrons reflecting or mirroring off of the surface of a flat substrate are complicated when compared to conventional straight-axis electron beam (e-beam) systems. Additional complications are presented because the electron beam passes twice through one or more electron lenses, once upon incidence and a second time upon reflection.
Due to these complications, a design including a plurality of lenses arranged along one straight axis is not practically feasible, and a beam separator is needed to split the incident and reflected beams. One implementation of a beam separator uses a prism with a single shaped magnetic field as a beam separator. For example, see E. Bauer, “Low energy electron microscopy,” Rep. Prog. Phys. 57 (1994), p. 895.
It is desirable to improve LEEM systems, including those utilized for the automated inspection or review of substrate surfaces. More particularly, it is desirable to improve LEEM systems with a tilt capability.